Where and how to rent a motobike/scooter in Jakarta?

I have never seen a formal motorbike rental business outside a tourist area, but it would be a very bad idea to rent anyway as your licence is unlikely to be valid and an accident or police stop could leave you in expensive trouble.

IMO you could ask around the local security guards or ojek. I have before, rented a bike locally from a family who seemed to have more bikes than kids and whilst it was a heap of junk it did the job  and the cash for the rental probably helped them as well. But if you don't have a SIM be very careful where you ride as the police have a tendency at times to stop all bikes. I managed a year without one and hated every trip due to the worry of being stopped. But being legal now it's OK for me.